1. Field of the Invention
The invention relates in general to a package structure, and more particularly to a package structure having a second protection layer.
2. Description of the Related Art
Referring to FIG. 1, a conventional package structure having a repassivation layer is shown. An ordinary package structure 10 includes a semiconductor device I2, a passivation layer 14, a repassivation layer 16, a plurality of solder bumps 18, a substrate 20 and a sealant 22. The surface of the semiconductor device 12 has a plurality of pads 12a used as terminals for electrical connection. The surface of the semiconductor device 12 is further covered by the passivation layer 14 which provides protection function and exposes a part of the pads 12a. 
Due to the smaller thickness, the ordinary passivation layer 14 may easily crack when receiving a force. In recent years, the repassivation layer 16 is further disposed on the passivation layer 14 of the package structure 10 to avoid the passivation layer 14 being cracked. The solder bumps 18 are connected to the semiconductor device 12 and the substrate 20 through a part of the exposed pads 12a. The sealant 22, interposed between the substrate 20 and the repassivation layer 16, encapsulates a plurality of solder bumps 18.
As the package is now being miniaturized, the minimum length of the pad 12a has been reduced to be smaller than 75 microns (μm). The package structure 10 formed by stacking the passivation layer 14 and the repassivation layer 16 further reduces the exposed area of the pads 12a, and the contact area between the solder bump 18 and the pads 12a is also reduced due to the repassivation layer 16. However, the force between the solder bumps 18 and the pads 12a increases as the contact area decreases, so that the package cannot pass the subsequent reliability test (such as temperature cycling). That is, the adhesion between the solder bumps 18 and the pad 12a decreases as the force increases, so that the solder bumps 18 cannot be tightly coupled to the pad 12a. 
Besides, as the material of the repassivation layer 16 is softer, the adhesion between the repassivation layer 16 and the sealant 22 is lower, so that the repassivation layer 16 cannot be firmly coupled to the sealant 22 or the solder bumps 18, hence preventing the semiconductor device 12 from being fixed on the substrate 20 firmly.